What tray do you have? I have the ULCS digital tray and arm.
I simply used a flat bottomed base loc line piece against the arm and screwed it in. Same for the strobe head. It's helpful to have a femae/female piece, too. On my Subal, I simply flipped a piece over so the big end of a normal piece is down against the housing plate. I noticed that the caused a little wriggle so I stuck a cut to size piece of yoga mat (any neoprene will work) under it and viola - perfection! I now have the proper piece, but what mess with what isn't broken?